In certain procedures, especially in certain medical procedures, injection syringes are utilized manually to express rather viscous fluids wherein the syringe assemblies must gain substantial mechanical advantage. Particularly in percutaneous vertebroplasty, bone implant material must be injected into a patient's vertebra for stabilization of the spine in osteoporosis and metastatic disease. The biocompatible implant material is viscous, and one such material is polymethylmethacrylate (PMMA). During the procedure, the hard cortical bone of the vertebra is penetrated by a needle such as a standard 11 gauge bone biopsy needle having a cannula and stylet, and then the stylet is removed; a syringe loaded with the bone cement is connected to the proximal end of the relatively narrow cannula; and the plunger is then actuated to express the cement through the cannula and out its distal end and into the intra-vertebral site. Preferably, a syringe containing 10 cc or more volume is utilized, since about 5 to 8 cc of implant material is required per implantation procedure.
In PCT Patent Publication WO 99/49819 is disclosed a high pressure applicator particularly useful in percutaneous vertebroplasty, said to permit the manual generation of about 1000 to 2000 psi of pressure or more, enabling the implant material to be more viscous than prior art syringes allowed which is preferred for the material to remain in place once applied in situ. The large storage capacity of the chamber of the device enables a complete implantation procedure to be performed expeditiously without reloading the device, and the applicator is said to be consistently controllable for an even, constant application of pressure during material delivery. A first column is open ended and defines a chamber for initial receipt of the implant material, and has exterior threads to cooperate with internal threads of a larger diameter second column extending from a rotatable actuator handle. A pressure seal such as an O-ring is provided at the distal end of the second column to seal with the outside surface of the first column for providing a high pressure seal to maintain the air between the first and second columns to enable generation of pressure therebetween during an application procedure. The distal end of the first column has attached thereto a Luer-lock connector to define a connection either to the cannula or to a flexible tube that is connected to the cannula, and a radially extending stabilizer is provided near the distal end of the first column for enabling the operator to grasp and steady the device as the actuator handle at the proximal end of the second column is rotated to generate pressure to the implant material within the chamber.
A similar product sold by Parallax Medical, Inc. of Mountain View, Calif., includes a plunger extending from the second column to move coaxially within the chamber of the first column to apply pressure to the implant material, and includes at the plunger's distal end an O-ring seal in a grooved seat forwardly of a ledge, to engage and compress against the chamber's inner surface as the plunger is moved further into the chamber to prevent implant material from passing therepast during an application procedure. The first column also includes an enlarged threaded open proximal end section, and a complementary second column, enabling better mechanical advantage and also permitting intentional overfill of the chamber proper to remove as much air as possible from the chamber proper once filled with implant material.
Another application device for applying bone cement (as well as mixing the two-part cement) is disclosed in U.S. Pat. No. 4,671,263, wherein a plunger distal end includes a pair of lamellae of flexible material that abut the inside surface of the casing or chamber, and are said to abut tightly enough such that as the plunger is moved distally the lamellae permit air to escape while preventing bone cement from passing. Pressures provided by the syringe are low and said to range from 2 bar to 20 bar (200 kPa to 2 Mpa; or 29.1 to 291 psi).
It is desired to provide a high pressure injection syringe that provides a seal at the proximal end of the chamber that assuredly inhibits passage therepast of viscous material, under pressures of at least 1000 psi (69 bar or 690 Mpa).
It is also desired to provide a high pressure injection syringe that not only provides for a seal under high pressure but also simplifies the air aspiration procedure and also reduces the length of time necessary for the application of the viscous material to the intended site.
It is further desired to provide a high pressure injection syringe that is adapted to manually and controllably generate higher pressures, which in turn permits increasing the viscosity of implant material for enhancing the effectiveness of medical procedures such as vertebroplasty.